T-LAYER® e TiN CVD



Fig.2: The aggression localized on T-Layer®
 Il T-Layer®, thanks to its chemical and physical properties may be a substitute of the steel in contact with aluminum and is a valid way to reduce sensibly this kind of problems. An interesting study executed by the Department of Material Engineering of the University of Trento on specimen in Aisi H11 hardened and tempered, showed the behavior of some surface treatments for quenching in melted aluminum. The alloy was made up by: 92,6% Al; 6,8% Si; 0,29% Mg; 0,17% Fe; 0,1% Ti; 0,02% Sr; the temperature was of 740-760 °C; the duration of 4 hours.

The experiment dealt with the following treatments: bare specimen (hardening and tempering only), nitriding, chrome nitride (CrN PVD), zirconium nitride (ZrN PVD), and, finally T-Layer®.

Bare specimen and nitrided specimen

The analysis underlined a general aggression to the surface and the melting of the surface zone. The quenching duration was probably too long to allow to find out differences between hardened and tempered specimen and bare ones. Anyway, thanks to the less wettability and the aggression mechanism, which may cause a preliminary dissolution of the iron nitride layers, we understand that the nitriding process has a positive effect on the Aisi H11 resistance to the aggression of the melted aluminum alloy.

Chrome nitride and zirconium nitride

Extremely higher were the results on PVD coating specimen. We noticed that aluminum alloy is not able to attack chemically, and therefore melt, the deposited nitride. The aggression was localized on some points where the cracks or other imperfections of the coating allowed an aluminum infiltration into the steel. In this case the increase of volume due to the production of intermetallic compounds causes a localized detachment of the coating and the alloy inflow directly on the steel. The result is globally positive because, after 4 hours, the aggression was still localized on some points and not generalized as for the other specimen. Zirconium nitride showed a better resistance than chrome nitride.